The robbery was reported shortly before 8:55 p.m. at the store located at 1691 Contra Costa Blvd., according to police.
The suspect entered the store and asked to see a Playstation 3 console. When an employee handed it to him, the suspect pepper sprayed him and ran toward the store's exit, police said.
A female employee tried to block the door but was also pepper sprayed by the suspect, who fled on foot from the store. He was not found by officers during a subsequent search.
The suspect is described as a black man who is between 25 to 30 years old, about 6 feet 2 inches tall, and weighs 200 pounds. He had facial hair, and was wearing dark clothing and a beanie, police said.
Anyone with information about the robbery is asked to call the Pleasant Hill Police Department's investigations division at (925) 288-4630.